The invention relates to a capacitive sensor element with a plurality of sensor fields, as they correspond for example to the arrangement on a touch screen. This capacitive sensor element comprises at least one multilayer body made up of two structured electrically conductive layers and an insulating layer in between. The invention also relates to a method for the production of such a sensor element.
Such capacitive sensor elements are known from DE 10 2011 115 851 A1. The sensor elements disclosed therein comprise for example conductive strips arranged according to the “bar and stripe” principle as electrodes. For example, wide conductive strips, “bars” or bar electrodes, which run—again for example—in the x-direction, lie on a first, lower electrically conductive layer, and narrow conductive strips, “stripes” or stripe electrodes, which run in the y-direction lie on a second electrically conductive layer arranged above the first. The two electrically conductive layers are galvanically separated by an insulating layer. At the crossover points of bars and stripes touch sensor fields, so-called touch fields, are formed.
The different geometrical formation of the electrodes as bars and stripes is favourable because of the course of the electric field lines between the conductive strips of the first and second electrically conductive layers. Because of the formation of the second electrically conductive layer as “stripes” there are many field lines which run through the space above the sensor element and which are disrupted by touching with the input element. The disruption of the course of the field lines corresponds to the input and can be determined more reliably by a greater number of disrupted field lines.
According to the previously known layouts for the electrically conductive layers of a capacitive sensor element, such as for example the layout known from DE 10 2011 115 851 A1, it is essential for reading the input signals that the first and second electrically conductive layers lie accurately one on top of the other. On the bar and stripe electrodes, connections are provided which transmit the signals from the sensor fields via corresponding plugs in an edge area of the module comprising the sensor element, with the result that an input can be clearly assigned and reliably read.
By “module” is meant here for example a Smartphone, an iPad or other touch screen. The sensor element forms at least a part of the input area of a touch screen and is preferably formed transparent.
The connections fit into plugs that are provided in the edge area of the sensor element. In order that the plugs also reliably make contact with the connections during assembly and thus all inputs can be read via the connections, it is necessary or at least advantageous for the reliability of the sensor element that the electrically conductive layers are laid accurately one on top of the other during assembly of the sensor element. In particular it is advantageous that the position of the two electrically conductive layers deviate for example by less than 200 μm, better still by less than 100 μm from their theoretically assigned location, at which the contacts to the plugs are provided. The tolerance limit during assembly of the previously known sensor elements can therefore be indicated as 200 μm or less.
This requirement of the production method is difficult to meet economically, which also makes assembly very expensive.